1. Field of the Invention
The present invention relates to antifuse devices. More particularly, the present invention relates to a double-half-via antifuse structure and to fabrication methods therefor.
2. The Prior Art
Antifuses have fallen into one of two categories. A first category of antifuse has a lower electrode formed from a doped region in a semiconductor substrate and an upper electrode formed in a conductive layer above the substrate. The conductive layer has comprised either a metal or a polysilicon layer. A second category of antifuse has its lower electrode located in a layer above and insulated from the sericonductor or other substrate. The lower and upper electrodes are typically formed from metals, most often comprising portions of two metal interconnect layers in the integrated circuit. Above-the-substrate antifuses often employ amorphous silicon as an antifuse material disposed in between the two conductive electrodes.
Numerous above-substrate antifuses are known in the art. Most such antifuses are metal-to-metal antifuses which are typically disposed between two metal interconnect layers in an integrated circuit. Examples of such antifuses are found in references such as U.S. Pat. No. 5,300,456 to Tigelaar et al., U.S. Pat. No. 4,914,055 to Gordon et al.
While above-the-substrate antifuses are useful devices, they tend to suffer from one or more problems including poor BVG (programming or breakdown voltage) control resulting from lack of control of the overetch of the amorphous silicon layer during the via etching of the thick interlayer dielectric separating the antifuse electrodes, and step coverage problems, etc.
It is thus an object of the present invention to provide an antifuse which has a lower sensitivity to etch selectivity during the antifuse via etching process.
Another object of the present invention is to provide an antifuse which avoids the problem of depositing an upper electrode material into a deep antifuse via.
Yet another object of the present invention is to provide an antifuse with improved BVG control.